Tools called reticles are used in the manufacture of semiconductor devices to optically expose circuit images on wafers. Often, twenty or more reticles may be required for processing a semiconductor wafer. Reticles commonly include a 6″×6″×¼″ thick or a 9″×9″×½″ thick optically clear quartz plate with a chrome image on the bottom side. Reticles also include a pellicle formed of a very thin transparent membrane for keeping particles away from the quartz surface and chrome image. The pellicle is typically mounted to a pellicle frame by adhesive such as glue. The pellicle frame is, in turn, adhered to the reticle plate. The particles will not be seen during the image exposure on the wafer as the particles will be kept out of the focal plane of the chrome image on the reticle plate.
A reticle stocker is usually employed to store large quantities of reticles. The reticles are often stored in an open fashion. This is called open or bare reticle storage and allows the highest density storage of reticles for long term storage. A typical reticle stocker will have a very clean or ultra clean air flow to prevent particles from adhering to the reticles in storage. A reticle stocker may also be designed to store reticle storage pods or shipping containers instead of storing reticles in open fashion. Robotic automation is often used to access the reticles stored inside the reticle stocker. The reticles are placed into reticle pods prior to leaving the stocker and can be placed onto automated transport vehicles for transport throughout the semiconductor facility.
In order to keep track of the reticles, identifying information is provided on the reticles which requires visual or optical reading. This often involves physical handling of the reticle which can generate particles or scratches on the reticle. Particles or scratches on reticles are undesirable in that the optical quality of the reticle can be reduced.